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Full text of "Text Book Of Mechanical Engineering"

672

Side-by-side: Early, Cut-off.

pressures have already been obtained for these points, and it only
remains to define their volumetric position. To do this take all
the points from 5 to 6 on the larger semi-circle, and transfer them
to the left side of the circle; thus B 6 is changed to B j. Pro-
jecting these downwards we only have to set up the heights
previously found, to complete the L. P. curve from P5 to P6.
The further expansion from P6 to PK is only in L. P. cylinder and
receiver. Therefore,

'45 + *3 + "7875

P, = 28-;

'45 + *3

177

or we have arrived at the residual pressure assumed at first.

III. Compound Engine with cranks at right angles; cut-off in
L. P. before half stroke. Referring to Fig. 659, and taking the
following data :

f H. P. = i                    Hc - -i

Volumes < L. P.   = 3                .    Lc   = '3'

IR.    = 1-5

Cut-off ... H.P. at -3,            L. P. at -4.

PB will be found to be 30*2, while PL is 18 as before. Pi = 44
by measurement. Then the drop to P2 is much less than that in
Fig. 658 because the receiver only is opened to H. P. cylinder,

and         ^       44 x ri 4 30-5 x ix

p    __ j_f________L_~_Jl_:___......_.      ^6'2

Compressing in H, P. and R,
i-i + 1-5

P3 = 36-2 x

= 44-8

ri 4 1*5

A sudden expansion occurs by opening to Lc, and

n       44'8 x (I 4 'I + i%\ + 18 x -3

p   =---------~.----------__- = 41-4

4              j + -i + 4 + -3

Then, while L. P. crank moves from 4 to 5 on the large circle,
the H. P. crank moves through a similar arc on the smaller circle,
at right angles to it, as before.    Taking volumes at P4 and P5 we
41-4 x {-5 + -i '+'1-5 + -3} _   g
i + -i + i-5 + -3 4 *6i     ~.3